Optical distribution system having time switch

ABSTRACT

Optical paths to propagate a plurality of optical information signals intersect optical paths to transmit light signals to a plurality of subscribers. Light power dividing and propagation direction changing devices for separating requested optical information signals are arranged at the intersecting points. Losses of the optical information signals, due to the separation, are compensated by optical amplification, so that the signals can be distributed to all of the subscribers while maintaining a predetermined intensity. Thus, the same photosignal can be distributed to a plurality of subscribers. The system can be easily expanded in correspondence to an increase in the number of optical information signals and an increase in the number of subscribers.

This application is a continuation of application Ser. No. 08/685,730filed 25, Jul. 1996, now abandoned, which is a division of applicationSer. No. 08/209,751 filed 9, Mar. 1994, now Pat. Ser. No. 5,576,872.

BACKGROUND OF THE INVENTION

The present invention relates to an optical device which is used in anoptical fiber communication system and, more particularly, to an opticaldevice which is suitable for an information distribution optical networkrepresented by a cable television and to a synthesizing method of suchan optical device.

Communication networks have been supported so far by electronic circuitstechniques (reference literature: Minoru Akiyama, et al., "DigitalTelephone Exchange", Sangyo Tosho Co., Ltd., published in 1986). Inrecent years, the development of optical fiber communication systemwhich can transmit information to a long distance at a high speed isremarkable and the realization of such optical communication systems isprogressing.

Among such systems information distribution type optical networks areadvancing in such a direction as to distribute a larger amount ofinformation to a larger number of terminals. In the case of opticalcable television as an example, there is a tendency to increase thenumber of channels and the number of subscribers increase. When thenumber of channels increases, it is necessary to widen a range of thesignal selection. According to a method of selecting the channel in areceiver which the subscriber possesses, it is difficult to cope with anincrease in number of channels. It is, therefore, necessary to use amethod whereby, on the side which serves information, the channelselection is controlled and only the necessary signal is distributed tothe subscriber in accordance with a request from the subscriber. Aconstruction to realize such a method by present existing devices is asshown in FIG. 2. Signals 1--1 to 1-m of respective channels aredistributed to selectors 3-1 to 3-n corresponding to subscribers (1 ton) by optical amplifying distributors 2-1 to 2-m. Distribution signals4-1 to 4-n selected by the selectors 3-1 to 3-n in accordance withrequest signals 5-1 to 5-n are sent to the subscribers.

Each of the optical amplifying distributors 2-1 to 2-m can be realizedby a combination of an optical amplifier and a photocoupler. As aselector of a photosignal, it is possible to apply an optical switch asdescribed in the literature, "Journal of Lightwave Technology", Vol. 9,No. 7, pages 871-877, 1991.

According to the above conventional method, since an increase in numberof subscribers or an increase in number of channels causes an increasein number of amplification distributions or an increase in number ofchannels which can be selected, there is a problem such that the scalesof the photocoupler for separation and the optical switch and theirconnecting wires increase. Since the signals of the channels which arenot selected are also amplified, there is also a problem such that anunnecessary electric power is consumed. There is further a problem suchthat it is necessary to exchange the optical switch to another opticalswitch having a larger number of inputs in association with an increasein number of channels and there is a problem of an expandability.According to the above conventional method, on the other hand, since itis necessary to use the amplification distribution and opticaltransmission path for the channel which is hardly selected, there is aproblem such that a whole scale increases due to the parts which arehardly used.

Another conventional technique is entitled "Optical Switch Element"disclosed in JP-A-61-91623. Such a technique relates to a method of lossmodulating each signal after the signals are distributed toward all ofthe output terminals, so that there is a problem such that the signalwhich is not selected is abandoned. For instance, since a separationloss occurs at every optical switch, even if the light intensity iscompensated by amplification, when the number of distributionsincreases, the S/N ratio deteriorates. Since the unnecessary signals arealso distributed, an intensity which is distributed to the signal to beselected decreases and a total amplification amount and an electricpower consumption increase. A further conventional technique is shown inKishimoto et al., "Optical Self-Routing Switch Using Integrated LaserDiode Optical Switch", IEEE Journal on selected areas in communication,Vol. 6, No. 7, August, 1988.

SUMMARY OF THE INVENTION

It is an object of the invention to reduce a scale of an opticaldistribution circuit by realizing both the separation and selection ofphotosignals by one optical device.

Another object of the invention is to suppress an electric powerconsumption by performing optical amplification according to the numberof subscribers selected.

Still another object of the invention is to provide an opticaldistribution circuit which can be easily expanded by merely adding newparts in correspondence to an increase in the number of channels.

Further another object of the invention is to provide a synthesizingmethod which can reduce a scale of an optical distribution circuit inconsideration of the probability of each channel being selected.

The above objects of the invention are accomplished by an opticaldistribution circuit in which optical distribution devices, eachcomprising two optical paths, a light power dividing and propagationdirection changing device which connects those optical paths, and anoptical amplifying unit are matrix connected in a manner such that thetwo optical paths correspond to rows and columns, respectively.

Other objects of the invention are accomplished by an opticaldistribution circuit which is constructed by an optical circuit in whichthe above optical distribution devices are connected to a (m1×n1)matrix, a (n1×n2) matrix, and a (m2×n2) matrix, wherein (n1) opticaloutputs of the (m1×n1) matrix optical circuit are connected to (n1)optical inputs of the (n1×n2) matrix optical circuit and (n2) opticaloutputs of the (n1×n2) matrix optical circuit are connected to (n2)optical inputs of the (m2×n2) matrix optical circuit.

According to the invention, the signal of each channel is inputted tothe optical path corresponding to each row and the signal of theselected channel is outputted from the optical path of each columncorresponding to the subscriber. In accordance with a request of eachsubscriber, the light power dividing and propagation direction changingdevice separates the signal of the channel to the optical pathcorresponding to the subscriber. The optical amplifying sectionfunctions so as to compensate a loss of signal intensity which wascaused by the signal separation.

According to the present invention, therefore, since both the separationand selection of the signal can be realized by one light power dividingand propagation direction changing device, the scale can be reduced.

Since the signal is amplified so as to compensate only the loss whichwas caused by the separation or propagation and the signal of thechannel which is not selected is not amplified, the electric powerconsumption can be suppressed.

Further, by constructing the optical distribution circuit in a matrixform, it is possible to expand in correspondence to an increase innumber of channels, an increase in number of subscribers, the row andcolumn. Thus, the expansion can be easily performed by using theexisting apparatus.

According to the optical distribution circuit comprising the (m1×n1)matrix optical circuit, (n1×n2) matrix optical circuit, and (m2×n2)matrix optical circuit, (m1) channels and (m2) channels can bedistributed to (n2) subscribers. The (m2×n2) matrix optical circuitenables all of the (n2) subscribers to request the (m2) channels whichare frequently requested. The (n1×n2) matrix optical circuit narrowsdown the number of subscribers who select the (m1) channels such thatthe total number of channels which are requested is equal to a smallnumber of (n1) or less from (n2) to (n1) or less (n1<n2). The (m1×n1)matrix optical circuit enables the narrowed-down (n1 or less)subscribers to select the (m1) channels.

According to the present invention, the distribution of (m1) channelswhich need the (m1×n2) matrix in the fundamental construction can berealized by a (m1×n1) matrix optical circuit and a (n1×n2) matrixoptical circuit, and thus, the scale can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fundamental constructional diagram of an opticaldistribution device according to the present invention;

FIG. 2 is a constructional diagram of a optical distribution circuitaccording to a conventional technique;

FIG. 3 is a constructional diagram of optical distribution devicesaccording to the invention;

FIG. 4 is a constructional diagram of an optical distribution devicehaving an optical amplifying section according to the invention;

FIG. 5 is a constructional diagram of an optical distribution devicehaving an optical amplifying section according to the invention;

FIG. 6 is a constructional diagram of an optical distribution circuitaccording to the invention;

FIG. 7 is a fundamental constructional diagram of light power dividingand propagation direction changing means according to the invention;

FIG. 8 is a constructional diagram of light power dividing andpropagation direction changing means including a variable partialreflecting mirror according to the invention;

FIG. 9 is a constructional diagram of light power dividing andpropagation direction changing means including an optical amplifyingsection according to the invention;

FIG. 10 is a constructional diagram of light power dividing andpropagation direction changing means including a fixed portionreflecting mirror according to the invention;

FIG. 11 is a constructional diagram of light power dividing andpropagation direction changing means including a variable totalreflecting mirror according to the invention;

FIG. 12 is a constructional diagram of an optical distribution devicehaving an optical amplifying section according to the invention;

FIG. 13 is a constructional diagram of an optical distribution devicehaving an optical amplifying section according to the invention;

FIG. 14 is a constructional diagram of an optical distribution devicehaving an optical amplifying section according to the invention;

FIG. 15 is a constructional diagram of an optical cable televisionsystem;

FIG. 16 is a constructional diagram of an optical distribution circuitaccording to the invention;

FIG. 17 is a constructional diagram of an optical distribution circuitaccording to the invention;

FIG. 18 is a constructional diagram of a signal distributor according tothe invention;

FIG. 19 is a constructional diagram of a signal distributor according tothe invention;

FIG. 20 is a constructional diagram of a composite signal distributoraccording to the invention;

FIG. 21 is a constructional diagram of a composite signal distributoraccording to the invention;

FIG. 22 is a constructional diagram of a composite signal distributoraccording to the invention;

FIG. 23 is a constructional diagram of a composite optical distributioncircuit according to the invention;

FIG. 24 is a constructional diagram of a composite optical distributioncircuit according to the invention;

FIG. 25 is a constructional diagram of a composite optical distributioncircuit according to the invention;

FIG. 26 is a constructional diagram of a composite optical distributioncircuit according to the invention;

FIG. 27 is a constructional diagram of a composite optical distributioncircuit according to the invention;

FIGS. 28A and 28B are a constructional diagram of an opticaldistribution circuit for a time division multiplex and a diagram showingsignal waveforms;

FIG. 29 is a constructional diagram of an optical distribution circuitfor wavelength division multiplex;

FIG. 30 is a constructional diagram of an optical distribution circuitaccording to the invention; and

FIG. 31 is a constructional diagram of a time switch according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As a first embodiment according to the present invention, FIG. 1 shows afundamental construction of an optical distribution device. An opticaldistribution device 10-1 comprises: a first optical path having anoptical input 11 and an optical output 13; a second optical path havingan optical input 12 and an optical output 14; and light power dividingand propagation direction changing means 20 arranged at an intersectingportion of the first and second optical paths. The light power dividingand propagation direction changing means 20 operates in two modes ofnon-separation/separation.

In the non-separation mode, a photosignal of the optical input 11 isoutputted to only the optical output 13 and is not outputted to theoptical output 14. Similarly, a photosignal from the optical input 12 isoutputted to only the optical output 14 and is not outputted to theoptical output 13. In the separation mode, on the other hand, thephotosignal from the optical input 11 is outputted to the optical output13 and a part of the photosignal is separated and is also outputted fromthe optical output 14. The photosignal from the optical input 12 in theseparation mode, on the other hand, is not outputted to the opticaloutput 13. In a system which is set into the separation mode only whenthe photosignal is not inputted from the optical input 12, however, thesystem can be also set into a state in which the photosignal whichpropagates in the optical input 12 can be separated to the opticaloutput 13. The output of the photosignal from the optical input 12 tothe optical output 14 in the separation mode operates in differentmanners in dependence on the system which is used and there is a casewhere such a photosignal is outputted and a case where it is notoutputted.

FIG. 3 shows a fundamental construction of an optical distributiondevice 10-2 according to the embodiment which is arranged in a (m×n)matrix form. The optical distribution device 10 comprises: (m) firstoptical paths; (n) second optical paths; and (m×n) light power dividingand propagation direction changing means 20 arranged at intersections ofthe first and second optical paths. The (m) first optical paths haveoptical inputs 11-1 to 11-m and optical outputs 13-1 to 13-m. The (n)second optical paths have optical inputs 12-1 to 12-n and opticaloutputs 14-1 to 14-n.

Each light power dividing and propagation direction changing means 20operates in the two modes of non-separation/separation. In thenon-separation mode, the photosignal which was propagated in the firstoptical path is outputted to only the first optical path and thephotosignal which was propagated in the second optical path is outputtedto only the second optical path. In the separation mode, on the otherhand, the photosignal which was propagated in the first optical path isoutputted to the first optical path and a part of the photosignal isseparated and is also outputted to the second optical path. Thephotosignal which was propagated in the second optical path in theseparation mode is not outputted to the first optical path. However, ina system which is set into the separation mode only when the photosignalis not propagated from the second optical path, the system can be alsoset into a state in which the photosignal which was propagated throughthe second optical path can be separated by the first optical path. Asfor the output to the second optical path of the photosignal from thesecond optical path to the second optical path in the separation mode,since a different operation is executed in dependence on a system whichis used, there is a case where the photosignal is outputted and a casewhere it is not outputted.

The photosignal distributing operation of the optical distributiondevice 10-2 will now be described with respect to the case ofdistributing the photosignal from the optical input 11-i to the opticaloutput 14-j as an example. Among light power dividing and propagationdirection changing means (20-i, j to 20-m, j) of the j-th column andlight power dividing and propagation direction changing means (20-i, 1to 20-i, n) of the i-th row, the light power dividing and propagationdirection changing means (20-i, j) operates in the separation mode andthe other light power dividing and propagation direction changing means20 of the i-th row operate in the non-separation mode. A photosignalfrom the optical input 11-i passes from the light power dividing andpropagation direction changing means (20-i, 1) which operates in thenon-separation mode or the separation mode through the light powerdividing and propagation direction changing means (20-i, (j-1)) andpropagates in the first optical path and reaches the light powerdividing and propagation direction changing means (20-i, j). Thephotosignal is separated to the second optical path by the light powerdividing and propagation direction changing means (20-i, j) whichoperates in the separation mode. The photosignal of the channel (i)which was separated passes from the light power dividing and propagationdirection changing means (20-(i+1),j) which operates in thenon-separation mode through the light power dividing and propagationdirection changing means (20-m, j) and is outputted from the opticaloutput 14-j.

In the first embodiment, since the signal to be selected is separated bythe light power dividing and propagation direction changing means 20,both of the separation and the selection of the signal can be realizedby one optical device. Therefore, the scale of the optical distributioncircuit can be reduced.

FIG. 4 shows a construction of an optical distribution device 10-3 as asecond embodiment according to the invention. The optical distributiondevice 10-3 comprises: a first optical path having the optical input 11,the optical output 13, and an optical amplifying section 16; a secondoptical path having the optical input 12 and the optical output 14; andthe light power dividing and propagation direction changing means 20arranged in the intersecting portion of the first and second opticalpaths. The light power dividing and propagation direction changing means20 and the optical amplifying section 16 operate in the two modes ofnon-separation/separation in accordance with a control signal 15.

In the non-separation mode, the photosignal of the optical input 11 isnot amplified by the optical amplifying section 16 but is outputted toonly the optical output 13 by the light power dividing and propagationdirection changing means 20 and is not outputted to the optical output14. Similarly, the photosignal from the optical input 12 is outputted toonly the optical output 14 and is not outputted to the optical output13. In the separation mode, on the other hand, the photosignal from theoptical input 11 is amplified by the optical amplifying section 16 andis outputted to the optical output 13 and a part of the photosignal isseparated and is also outputted to the optical output 14. The output tothe optical output 14 of the photosignal from the optical input 12 inthe separation mode differs in dependence on the system in a mannersimilar to the case of the first embodiment.

In the second embodiment, the signal can be amplified in the opticalamplifying section 16 so as to compensate for separation loss which iscaused by separating the photosignal in the light power dividing andpropagation direction changing means 20. Since there is no need toamplify the photosignal which is not separated, electric powerconsumption can be suppressed.

FIG. 5 shows a construction of an optical distribution device 10-4 as athird embodiment according to the present invention. The opticaldistribution device 10-4 comprises: a first optical path having theoptical input 11, optical output 13, and optical amplifying section 16;a second optical path having the optical input 12, optical output 14,and an optical amplifying section 17; and the light power dividing andpropagation direction changing means 20 arranged in the intersectingportion of the first and second optical paths. The light power dividingand propagation direction changing means 20 and the optical amplifyingsection 16 operate in the two modes of non-separation/separation inaccordance with the control signal 15.

In the non-separation mode, the photosignal of the optical input 11 isoutputted to only the first optical path in the light power dividing andpropagation direction changing means 20 and is amplified in the opticalamplifying section 16 so as to compensate a propagation loss amount. Thephotosignal of the same intensity as that of the optical input 11 isoutputted to the optical output 13 and is not outputted to the opticaloutput 14. Similarly, the photosignal from the optical input 12 isamplified in the optical amplifying section 17 so as to compensate apropagation loss amount and is outputted to only the second optical pathin the light power dividing and propagation direction changing means 20.The photosignal of the same intensity as that of the optical input 12 isoutputted to the optical output 14 and is not outputted to the opticaloutput 13. In the separation mode, on the other hand, the photosignalfrom the optical input 11 is amplified in the optical amplifying section16, the photosignal of the same intensity as that of the optical input11 is outputted to the optical output 13, and a part of the photosignalis separated and is also outputted to the optical output 14. Thephotosignal from the optical input 12 in the separation mode isamplified in the optical amplifying section 17 at a fixed amplificationgain. However, the operation in the light power dividing and propagationdirection changing means differs in dependence on the system in a mannersimilar to the case of the first embodiment.

In the third embodiment, the signal of the optical input 11 is outputtedfrom the optical output 13 as a photosignal of the same intensityirrespective of the mode of non-separation/separation. Similarly, thesignal of the optical input 12 is outputted from the optical output 14as a photosignal of the same intensity.

An embodiment of an optical distribution circuit 6-1 according to theinvention will now be described. Optical distribution devices 10 of (m)rows (m≧1) and (n) columns (n≧1) are arranged to (k) rows (k≧1) and (h)columns (h≧1) and are connected, thereby forming the opticaldistribution circuit 6-1. FIG. 6 shows a construction of the opticaldistribution circuit in the case where n=m=k=2 and h=3. The informationsignals 1--1 to 1-4 which are inputted to the optical distributioncircuit are inputted to the optical inputs 11 of the opticaldistribution devices (10-1,1) and (10-1,2) of the first column. Theoptical outputs 13 of the optical distribution devices of each column(first and second columns) are connected to the corresponding opticalinputs 11 of the next columns (second and third columns). The opticaloutput 13 of the last column (third column) is not connected. Theoptical input 12 of the first row is also not connected. The opticaloutput 14 of each row (first row) is connected to the optical input 12of the next row (second row). The optical output 14 of the last row(second row) is set to the optical outputs 4-1 to 4-6 to thesubscribers. Thus, the optical distribution circuit of four inputs andsix outputs can be constructed.

According to the embodiment, photosignals of an arbitrary four channelscan be distributed to six subscribers. The photosignal of the samechannel can be also distributed to a plurality of subscribers.

According to the embodiment, by increasing the value of (h), the numberof channels can be increased and, by increasing the value of (k), thenumber of subscribers can be increased. By connecting the opticaldistribution device 10 to the optical input 12 of the first column whichis not connected or to the optical output 13 of the last column (thirdcolumn) which is not connected, the circuit scale can be easilyexpanded.

When expanding the scale of the optical distribution circuit 6, thepropagation loss on the optical path and the separation loss in thelight power dividing and propagation direction changing means 20 cause alimitation due to attenuation of the intensity of the photosignal. Inthe second embodiment of the invention, since the separation loss can becompensated, a limit of the scale expansion can be widened. In the thirdembodiment, when the optical distribution device 10-4 is connected inthe matrix, the intensity of the photosignal which propagates in thefirst optical path is not attenuated due to the operation of the opticalamplifying section 16. Similarly, the intensity of the photosignal whichpropagates in the second optical path is also not attenuated due to theoperation of the optical amplifying section 17. Therefore, when thenumber of columns and the number of rows are increased, a limitation dueto the losses by the separation or propagation on the first and secondoptical paths can be eliminated.

A specific constructional example of the light power dividing andpropagation direction changing means 20 will now be described. The mostfundamental construction relates to a method of changing the propagationdirection of the photosignal by using a partial reflecting mirror whichcan control a reflectance. FIG. 7 is a constructional diagram of a firstlight power dividing and propagation direction changing means 20-1. Themeans 20-1 comprises: a first optical path connecting the optical input11 and the optical output 13; a second optical path connecting theoptical input 12 and the optical output 14; and a variable partialreflecting mirror 21 which is arranged at an intersecting point of thefirst and second optical paths and is controlled by the control signal15. In the non-separation mode, since the variable partial reflectingmirror 21 transmits the photosignal, the photosignals from the opticalinputs 11 and 12 are outputted from the optical outputs 13 and 14,respectively. In the separation mode, since the variable partialreflecting mirror 21 partially reflects the photosignal, the photosignalfrom the optical input 11 is separated and outputted from the opticaloutput 14. Since the variable partial reflecting mirror 21 partiallyreflects the photosignal, the photosignal from the optical input 12 isalso outputted from the optical output 13.

According to the embodiment, a part of the photosignal which is inputtedto the first optical path can be separated and taken out to the secondoptical path.

There is a method of connecting the first and second optical paths by athird optical path, thereby converting the propagation direction twiceat two connecting points. FIG. 8 is a constructional diagram of a secondlight power dividing and propagation direction changing means 20-2.

The means 20-2 comprises: a first optical path connecting the opticalinput 11 and the optical output 13; a second optical path connecting theoptical input 12 and the optical output 14; and a third optical pathconnected to the first and second optical paths. The variable partialreflecting mirror 21 which is controlled by the control signal 15 isarranged at each of the intersecting point of the first and thirdoptical paths and the intersecting point of the third and second opticalpaths. In the non-separation mode, since the variable partial reflectingmirror 21 transmits the photosignal, the photosignals from the opticalinputs 11 and 12 are outputted from the optical outputs 13 and 14,respectively. In the separation mode, since the variable partialreflecting mirror 21 partially reflects the photosignal, the photosignalfrom the optical input 11 is separated and is propagated in the thirdoptical path and is again separated and is propagated in the secondoptical path and is outputted from the optical output 14. A part of thephotosignal from the optical input 12 is transmitted and is outputtedfrom the optical output 14 but is not outputted to the optical output13. Such device can be realized by the same structure as that disclosedin, for example, FIGS. 2A to 2C in the U.S. Pat. No. 5,044,745, which isincorporated herein by reference.

By reflecting the photosignal twice as in the embodiment, thephotosignal which is inputted to the second optical path is notseparated to the first optical path. Consequently, the photosignal onthe second optical path is not mixed with the photosignal on the firstoptical path.

By arranging the variable partial reflecting mirror 21 at theintersecting point of the third and second optical paths in theembodiment, a wavelength multiplex signal can be outputted from theoptical output 14.

Further, by optically amplifying the separated signal, an S/N ratio ofthe separated photosignal can be improved. FIG. 9 is a constructionaldiagram of a third light power dividing and propagation directionchanging means 20-3.

The embodiment has a construction in which an optical amplifying section22 which is controlled by the control signal 15 is arranged on the thirdoptical path of the second light power dividing and propagationdirection changing means 20-2. In the non-separation mode, since thevariable partial reflecting mirror 21 transmits the photosignal in amanner similar to the second light power dividing and propagationdirection changing means 20-2, the photosignals from the optical inputs11 and 12 are outputted from the optical outputs 13 and 14,respectively. In the separation mode, since the variable partialreflecting mirror 21 partially reflects the photosignal, the photosignalfrom the optical input 11 is separated and is propagated in the thirdoptical path and is amplified in the optical amplifying section 22. Thesignal is separated in the next variable partial reflecting mirror 21and is propagated in the second optical path and is outputted from theoptical output 14. A part of the photosignal from the optical input 12is transmitted and is outputted from the optical output 14 but is notoutputted to the optical output 13. Such a device can be realized by thesame structure as that disclosed in, for example, FIGS. 1A and 1B inU.S. Pat. No. 5,044,745.

By optically amplifying the photosignal just after the separation as inthe embodiment, there is an effect such that a high S/N ratio of theseparated output photosignal can be maintained. As a result, the minimumpermission intensity of the separated photosignal can be decreased, sothat there is an effect such that a reflectance of the variable partialreflecting mirror 21 can be reduced.

Subsequently, the optical amplifying section 22 has a function to absorband attenuate the photosignal in the non-separation mode. Even if thephotosignal is separated and is propagated in the third optical path, itis not propagated to the second optical path in the non-separation mode.Therefore, the separation of the signal can be realized by using a fixedpartial reflecting mirror. FIG. 10 is a constructional diagram of afourth light power dividing and propagation direction changing means20-4.

The embodiment has a structure in which the variable partial reflectingmirror 21 arranged at the intersecting point of the first and thirdoptical paths of the third light power dividing and propagationdirection changing means 20-3 is replaced by a fixed partial reflectingmirror 23. The photosignal from the optical input 12 is outputted toonly the optical output 14 and is not outputted to the optical output 13irrespective of the non-separation/separation mode in a manner similarto the second light power dividing and propagation direction changingmeans. In the non-separation mode, the photosignal from the opticalinput 11 is outputted to the optical output 13 and is also separated tothe third optical path by the fixed partial reflecting mirror 23. Sincethe optical amplifying section 22 in the non-separation mode absorbs andattenuates the photosignal, the signal is not outputted to the opticaloutput 14. In the separation mode, the photosignal is outputted to theoptical output 13 by the fixed partial reflecting mirror 23 and is alsoseparated to the third optical path. In the separation mode, since theoptical amplifying section 22 amplifies the photosignal, the variablepartial reflecting mirror 21 partially reflects the photosignal, so thatthe signal is again separated and is propagated in the second opticalpath and is outputted from the optical output 14.

By using a reflecting mirror having a fixed reflectance as in theembodiment, the intensity loss by the separation and propagation whichis caused for a time interval until the photosignal from the opticalinput 11 is outputted from the optical output 13 is made constantirrespective of the non-separation/separation mode. This indicates thatthe optical amplifier of a fixed amplification gain can be used in theoptical amplifying section to maintain the intensity of the photosignalwhich is propagated in the first optical path constant.

In the structure according to the embodiment in which the variablepartial reflecting mirror 21 arranged at the intersecting point of thethird and second optical paths of the fourth light power dividing andpropagation direction 20-4 is replaced by the fixed partial reflectingmirror 23, the light intensity loss of the second optical path can bemade constant.

Further, the variable partial reflecting mirror which is arranged at theintersecting point of the third and second optical paths can be replacedby a variable total reflecting mirror. FIG. 11 is a constructionaldiagram of a fifth light power dividing and propagation directionchanging means 20-5.

The embodiment has a structure in which the variable partial reflectingmirror 21 arranged at the intersecting point of the third and secondoptical paths of the fourth light power dividing and propagationdirection changing means 20-4 is replaced by a variable total reflectingmirror 24. In the operation in the non-separation mode, in a mannersimilar to the fourth light power dividing and propagation directionchanging means 20-4, the photosignal from the optical input 11 issubjected to a predetermined loss and is outputted from the opticaloutput 13 and the photosignal from the optical input 12 is transmittedthrough the variable total reflecting mirror 24 and is outputted fromthe optical output 14. In the separation mode, the photosignal from theoptical input 11 is outputted to the optical output 13 and is separatedto the third optical path by the fixed partial reflecting mirror 23.Since the optical amplifying section 22 in the separation mode amplifiesthe photosignal, the variable total reflecting mirror 24 totallyreflects the photosignal, so that the signal is again separated and ispropagated in the second optical path and is outputted from the opticaloutput 14. On the other hand, the photosignal from the optical input 12in the separation mode is totally reflected by the variable totalreflecting mirror 24, so that it is not outputted to the optical output14.

By arranging the variable total reflecting mirror at the intersectingpoint of the third and second optical paths as in the embodiment, thephotosignal from the optical input 12 is not outputted to the opticaloutput 14 in the separation mode. This indicates that the apparatus canhave a function such that the signal on the downstream side on thesecond optical path (input signal of a large row number) can bepreferentially outputted than the signal on the upstream side (inputsignal of a small row number).

A compensating method of the light intensity will now be described. Anembodiment of an optical distribution device 10-5 shown in FIG. 12 has aconstruction in which an optical amplifying section 16-1 is arranged incorrespondence to each light power dividing and propagation directionchanging means 20. Each optical amplifying section 16-1 varies itsamplification gain in accordance with the control signal 15, whichcontrols the corresponding light power dividing and propagationdirection changing means 20, thereby making the optical loss in each ofthe non-separation/separation modes constant. Although the opticalamplifying section 16-1 has been arranged at the front stage of thelight power dividing and propagation direction changing means 20 in FIG.12, a similar effect is also obtained by arranging the opticalamplifying section 16-1 at the post stage of the light power dividingand propagation direction changing means 20.

An embodiment of an optical distribution device 10-6 shown in FIG. 13has a construction in which a light intensity detecting section 18 isarranged just before the optical output 13 of each of the first opticalpaths and an optical amplifying section 16-2 is arranged just after theoptical input 11 of each of the first optical paths. In order to makethe light intensity, which is detected by the light intensity detectingsection 18, constant, it is negatively fed back to an amplification gainof the optical amplifying section 16-2. Due to this, the number ofoptical amplifying sections can be reduced and an output light intensitycan be stabilized without being influenced by a variation or fluctuationof separation loss characteristics of the light power dividing andpropagation direction changing means 20. In FIG. 13, although theoptical amplifying section 16-2 has been arranged just after the opticalinput 11, for example, by arranging the optical amplifying section 16-2at a position on the first optical path and before the light intensitydetecting section 18 like a position after the light power dividing andpropagation direction changing means 20 of the last column and justbefore the light intensity detecting section 18, a similar effect isobtained.

An embodiment of an optical distribution device 10-7 shown in FIG. 14relates to an embodiment using optical amplifying sections 16-3 and 17each having a fixed amplification gain. As each light power dividing andpropagation direction changing means 20, a light power dividing andpropagation direction changing means 20 in which a separation ratio toseparate the photosignal from the first optical path is not changed inaccordance with the two non-separation and separation modes is used likea light power dividing and propagation direction changing means 20-4shown in FIG. 10 or the light power dividing and propagation directionchanging means 20-5 shown in FIG. 11. Since the total loss of thephotosignal which is propagated in the first optical path is constant, amethod of making the output light intensity almost coincide with theoptical input intensity can be realized by optically amplifying with theoptical amplifying section 16-3 at a predetermined amplification gain.In the embodiment, since the optical amplifying section 17 of the fixedamplification gain is also arranged on the second optical path, the lossof the photosignal which is propagated on the second optical path can bealso compensated.

Both of the light power dividing and propagation direction changingmeans 20 and optical amplifying sections 16 and 17 in the invention canbe realized by devices made of a semiconductor material. The variablepartial reflecting mirror 21 and variable total reflecting mirror 24 cancontrol reflectance characteristics by using a refractive index which ischanged by a carrier implantation amount. Further, as a change inamplification gain of each of the optical amplifying sections 16 and 22as well, a light amplification gain of an optical active portion can becontrolled by controlling a carrier implantation amount.

Integration can be easily accomplished by using a semiconductormaterial.

The use of the partial reflection denotes that it is sufficient to set arequired refractive index change amount to a value which is smaller thanthat in case of the total reflection, so that a driving electric powerof the control signal can be reduced. Further, since a conversion anglein the propagation direction can be set to a large value, an angle whichis formed by the first and second optical paths can be set to a largevalue. When the interval between the first and second optical paths isconstant, the interval of the light power dividing and propagationdirection changing means 20 is small, so that the device size can bealso reduced.

The optical distribution circuit 10 of the present invention can beapplied to an optical cable television system as shown in FIG. 15. Asignal distribution station 100 distributes the photosignal requestedfrom an information signal 1 of each channel as an optical distributionsignal 4 by optical lines 101 in accordance with a request signal 5which is transmitted from each terminal 102 for a subscriber via theoptical line 101.

In the signal distribution station 100, the request signal 5 from theterminal 102 for a subscriber is sent to a request control circuit 7 bya bidirectional photosignal separator 8. The request control circuit 7sends the control signal 15 to the optical distribution circuit 10 inaccordance with the request signal 5. The photosignal which wasrequested from a plurality of light information signals 1 in accordancewith the control signal 15 is outputted by the optical distributioncircuit 10 as a distribution signal 4 of the light from the light outputcorresponding to the subscriber who requested it. The light distributionsignal 4 passes through the bidirectional photosignal separator 8 and isoutputted to the optical line 101. The subscriber receives the lightdistribution signal 4 which was transmitted via the optical line 101 byterminal 102 for the subscriber, and can watch and listen to the programof the channel which was requested.

Since the embodiment uses the optical distribution circuit 10 of theinvention, the following effects are obtained. In the case where aplurality of subscribers requested the same channel, the lightinformation signal 1 of the same channel can be distributed to theplurality of subscribers. In the case where the number of channels whichprovide services is increased, by arranging additional opticaldistribution circuits 10 in the column direction, the system can beeasily expanded while using the conventional optical distributioncircuit 10 as it is.

In an optical cable television system to which the invention is applied,when the number of channels which provide services and the number ofsubscribers increase, there is a problem such that in the case of usingthe optical distribution circuit having a structure of the matrix typeswitch as it is, its scale increases in proportion to both of theincreased channels and subscribers. It is considered that an increase innumber of channels results in an enlargement of a scale of the system.The system can also provide services to channels which are hardlyselected. To construct a more efficient optical distribution circuit,there is considered a connecting method of the optical distributioncircuit such that only the requested channel among a number of channelsprepared is connected to the optical distribution circuit which can beselected by the subscriber.

A scale of an optical distribution circuit 6 can be suppressed to asmall scale by combining an optical distribution device 10-8 whichselects the signal from a number of channels and an optical distributiondevice 10-9 for distributing to the subscriber. FIG. 16 shows anembodiment regarding a synthesizing method of an optical distributioncircuit 6-2 using one optical distribution device 10--10. Fiveinformation signals 1 are inputted to the optical inputs 11 of theoptical distribution device 10-8 of the matrix type of (4×2) and to theoptical input 11 of the optical distribution device 10-9 of the matrixtype of (1×4). The signals from the optical outputs 14 of the opticaldistribution device 10-8 are inputted to the optical inputs 11 of theoptical distribution device 10--10 of the matrix type of (2×4). Signalsfrom the optical outputs 14 of the optical distribution device 10--10are inputted to the optical inputs 12 of the optical distribution device10-9. The signals from the optical outputs 14 of the opticaldistribution device 10-9 are outputted as distribution signals 4 of thelight from the optical distribution circuit 6-2.

The information signal 1 which was inputted to the optical input 11 ofthe optical distribution device 10-9 is a signal which is frequentlyselected and the signal can be distributed to all of the subscribers. Onthe other hand, the four signals inputted to the optical distributiondevice 10-8 are not so frequently selected, so that three or more ofthose four information signals 1 are not simultaneously selected. In theoptical distribution device 10-8, two signals which are outputted fromthe optical outputs 14 among the four signals inputted to the opticalinputs 11 can be selected by the subscriber.

To distribute the five information signals 1 to the four distributionsignals 4 by the matrix type optical distribution circuit, an opticaldistribution circuit of the matrix type of (5×4) is needed. However,such an optical distribution circuit is realized by combining opticaldistribution circuits of a small scale. Although the embodiment has beenshown as a small scale such that the five information signals 1 aredistributed to the four distribution signals 4, when the number ofchannels and the number of subscribers increases, the effect to reducethe scale becomes remarkable.

The effect to reduce the scale exists in the connection of the opticaldistribution devices 10-8 and 10--10. The details of such an effect willbe finally described with reference to FIG. 30.

FIG. 17 shows an embodiment of an optical distribution circuit 6-3 whichis constructed by further using a plurality of optical distributioncircuits of a small scale. In a manner similar to the opticaldistribution circuit 6-2 shown in FIG. 16, the scale of the opticaldistribution circuit 6 can be suppressed to a small scale by combiningthe optical distribution device 10-8 which selects the signal from anumber of channels and the optical distribution device 10-9 todistribute to the subscribers.

FIG. 17 shows the embodiment in which two optical distribution devices10-11 of the (1×2) matrix type are used in place of the one opticaldistribution device 10--10 of the (2×4) matrix type used in FIG. 16. Theinformation signals 1 are inputted to the optical inputs 11 of theoptical distribution device 10-8 of the (4×2) matrix type and to theoptical input 11 of the optical distribution device 10-9 of the (1×4)matrix type. Two signals from the optical outputs 14 of the opticaldistribution device 10-8 are inputted to the optical inputs 11 of thetwo optical distribution devices 10-11. The signals from two opticaloutputs 14 of each of the optical distribution devices 10-11 areinputted to four optical inputs 12 of the optical distribution device10-9. Signals from the optical outputs 14 of the optical distributiondevice 10-9 are outputted as distribution signals 4 of the light fromthe optical distribution circuit 6-2.

In the embodiment, the information inputted to the optical distributiondevice 10-8 which is hardly selected can be selected by one of thesubscribers of the first and second columns and by one of thesubscribers of the third and fourth columns.

According to the embodiment, the connecting portion which is realized bythe optical distribution device 10--10 of the (2×4) matrix type in theoptical distribution circuit 6-2 shown in FIG. 16 is realized by the twooptical distribution devices 10-11 of the (1×2) matrix type, so that thecircuit scale can be further suppressed to a small scale. Although theembodiment has been shown as a small scale such that five informationsignals 1 are distributed to four distribution signals 4, when thenumber of channels and the number of subscribers are increased, theeffect to reduce the scale becomes further remarkable. The number ofoptical distribution devices is not limited to 2 but the use of afurther larger number of optical distribution devices also produces theeffect of reducing the scale. Moreover, a plurality of opticaldistribution devices 10-11 can be also realized by using devices of adifferent scale so long as they satisfy a condition such that the totalnumber of optical inputs 11 is larger than the number of optical outputs14 from the device 10-8 and the total number of optical outputs 14 islarger than the number of optical inputs to the device 10-9.

The connecting method of suppressing an enlargement of the scale bycombining the optical distribution devices 10 can be also applied to theconventional distribution switch. In the general distribution switch,however, the inputs and outputs corresponding to the optical inputs 12and optical outputs 13 in the optical distribution devices 10 cannot bealways used. Therefore, it is necessary to partially change theconstruction as follows. In the case of using the optical input 12, theconnecting portion with the optical output 14 of the opticaldistribution device 10 of the preceding row is integrated. In the caseof using the optical output 13, the signal which is inputted ispreviously separated and distributed to the input of each distributionswitch. FIGS. 18 and 19 show embodiments of a signal distributioncircuit 30 using general distribution switches corresponding to theoptical distribution circuits 6 in FIGS. 16 and 17.

A signal distribution circuit 30-1 shown in FIG. 18 comprises: adistribution switch 31-1 having four information signal inputs 32 andtwo distribution signal outputs 33; and a distribution switch 31-2having three information signal inputs 32 and four distribution signaloutputs 33. Four of the five information signals 1 are inputted to thefour information signal inputs 32 of the distribution switch 31-1. Theremaining one information signal 1 and outputs from the two distributionsignal outputs 33 of the distribution switch 31-1 are inputted to thethree information signal inputs 32 of the distribution switch 31-2. Theoutputs from the four distribution signal outputs 33 of the distributionswitch 31-2 are outputted as four distribution signals 4 from the signaldistribution circuit 30.

In the embodiment, the information signal 1 which is directly inputtedto the distribution switch 31-2 which is frequently selected can bealways distributed to an arbitrary subscriber. The signal distributioncircuit 30 can select an arbitrary two of the four information signals 1which are inputted to the distribution switch 31-1 which is hardlyselected and can distribute the selected two signals 1 to arbitrarysubscribers.

In order to distribute the five information signals 1 to the fourdistribution signals 4 by the matrix type switch, a switch of the (5×4)matrix type is needed. However, such a switch is realized by combiningswitches of a small scale. Although the embodiment has been shown as asmall scale such that the signals are distributed to the fourdistribution signals 4, when the number of channels and the number ofsubscribers increase, the effect to reduce the scale becomes remarkable.

Further, FIG. 19 shows an embodiment which can be realized by using twodistribution switches 31-3 of a scale smaller than that of thedistribution switch 31-2.

A signal distribution circuit 30-2 comprises: the distribution switch31-1 having four information signal inputs 32 and two distributionsignal outputs 33; and the two distribution switches 31-3 having twoinformation signal inputs 32 and two distribution signal outputs 33.Four of the five information signals 1 are inputted to the fourinformation signal inputs 32 of the distribution switch 31-1. Theremaining one information signal 1 is distributed to two signals and areinputted to one of the two information signal inputs 32 of each of thetwo distribution switches 31-3. Signals from the two distribution signaloutputs 33 of the distribution switch 31-1 are inputted to the remainingone of the two information signal inputs 32 of each of the twodistribution switches 31-3. Signals from the four distribution signaloutputs 33 of the two distribution switches 31-3 are outputted as fourdistribution signals from the signal distribution circuit 30.

According to the embodiment, the information signal 1 which is directlyinputted to the distribution switch 31-3 which is frequently selectedalways can be distributed to an arbitrary subscriber. An arbitrary oneof the four information signals 1 which are inputted to the distributionswitch 31-1 which is not so frequently selected is selected by each ofthe two distribution switches 31-3 and can be distributed to eachsubscriber.

In order to distribute the five information signals 1 to the fourdistribution signals 4 by a matrix type switch, a switch of the (5×4)matrix type is needed. However, such a switch is realized by combiningswitches of a small scale. Although the embodiment has been shown as asmall scale such that the signals are distributed to four distributionsignals 4, when the number of channels and the number of subscribersincrease, the effect of reducing the scale becomes remarkable. Althoughthe two distribution switches 31-3 have been used in the embodiment, theeffect of reducing the scale becomes remarkable by using a furtherlarger number of distribution switches.

When information to be distributed and subscribers are classified inassociation with a variety of kinds of services of cable television, thesignal distribution circuit and the optical distribution circuit areused in a composite form. An embodiment of the composite signaldistribution circuit and optical distribution circuit will now bedescribed.

FIG. 20 shows a construction of an embodiment of a compositedistribution circuit 34-1 in which an information signal which is not sofrequently used is selected a plurality of times. The compositedistribution circuit 34-1 comprises three signal distribution circuits30. Four information signals 1 are inputted to a signal distributioncircuit 30-3 and one of them is selected and outputted. The one signaloutputted from the signal distribution circuit 30-3 and the twoinformation signals 1 are inputted to a signal distribution circuit30-4. The signal distribution circuit 30-4 selects two of the threeinputted signals and outputs. The two signals outputted from the signaldistribution circuit 30-4 and the one information signal 1 are inputtedto a signal distribution circuit 30-5. An arbitrary one of the threeinputted signals is selected and outputted as a distribution signal 4from each output of the signal distribution circuit 30-5.

Since the signal selecting process has been executed a plurality oftimes in the embodiment, particularly, in a system which serves a numberof kinds of information in which the number of opportunities ofselection is small, the switch scale can be effectively reduced.

FIG. 21 is a constructional diagram of an embodiment of a compositedistribution circuit 34-2 in which the information signals 1 selected bya plurality of signal distribution circuits 30-6, 30-7 are inputted inparallel to the signal distribution circuit 30-8 which outputs thedistribution signals 4.

The composite distribution circuit 34-2 comprises three signaldistribution circuits 30-6, 30-7, and 30-8. Four information signals 1are inputted to the signal distribution circuit 30-6. Two informationsignals 1 are inputted to the signal distribution circuit 30-7. One ofthe information signals 1 is selected and outputted by each of thesignal distribution circuits 30-6 and 30-7. One signal which isoutputted from each of the signal distribution circuits 30-6 and 30-7and another information signal 1 are inputted to the signal distributioncircuit 30-8. An arbitrary one of the inputted three signals is selectedand outputted as a distribution signal 4 from each output of the signaldistribution circuit 30-8.

In the embodiment, since different kinds of information signals can beselected by the signal distribution circuit suitable for them, the scalecan be effectively reduced in a system for distributing a variety ofinformation.

FIG. 22 shows a construction of an embodiment of a compositedistribution circuit 34-3 for distributing signals to different kinds ofsubscribers by a plurality of signal distribution circuits 30.

The composite distribution circuit 34-3 comprises two signaldistribution circuits 30-9 and 30-10. The inputted information signals 1are separated and inputted to the signal distribution circuits 30-9 and30-10. Each of the signal distribution circuits 30-9 and 30-10 outputsthe distribution signals 4 to the subscribers.

According to the invention, by using the signal distribution circuits 30in correspondence to the differences of channel selection frequencieswhich differ in dependence on the differences among the kinds ofsubscribers, the enlargement of the switch scale can be suppressed.

As signal distribution circuits 30 in the composite distribution switch34 of the invention, arbitrary conventional switches including thesignal distribution circuits 30-1 and 30-2 in the embodiment can beused.

FIGS. 23, 24, and 25 show constructions of composite opticaldistribution circuits 40-1, 40-2, and 40-3 corresponding to thecomposite distribution circuits 34-1, 34-2, and 34-3, respectively.

The constructions, operations, and effects of those composite opticaldistribution circuits are similar to those of the above compositedistribution circuits. As optical distribution circuits 6 which are usedin the composite optical distribution circuits 40-1 to 40-3, the opticaldistribution circuits 6-1 to 6-4 can be used. The number of inputs andthe number of outputs of each optical distribution circuit 6 are notlimited to the numbers shown in the embodiments but an opticaldistribution circuit 6 having a larger number of inputs and outputs canbe also used.

FIG. 26 is a constructional diagram of a composite optical distributioncircuit 40-4 having the same function as that of the composite opticaldistribution circuit 40-3. The inputted information signals 1, however,are inputted to an optical distribution circuit 6-11. Photosignals 41from the optical outputs 13 of the optical distribution devices 10constructing the optical distribution circuit 6-11 are inputted to anoptical distribution circuit 6-12. In a manner similar to the compositeoptical distribution circuit 40-3, the distribution signals 4 which areoutputted from the composite optical distribution circuit 40-4 aresignals which are outputted from the optical distribution circuits 6-11and 6-12.

Since the embodiment can be realized by connecting a plurality ofoptical distribution circuits in place of separating the signals anddistributing to a plurality of optical distribution circuits, theoptical lines can be simplified.

In a system of an optical cable television, a program rating of eachchannel changes in dependence on a time zone or a day of the week. In asystem in which a frequency at which an information signal is selectedchanges, when the selection frequency of the input information ismatched with the maximum time zone, a capacity and a scale of the systemare enlarged. By exchanging the channel whose selection frequency wasraised and the channel whose selection frequency was reduced inaccordance with the time zone, the enlargement of the scale of theoptical distribution circuit can be suppressed. FIG. 27 shows anembodiment of an optical distribution circuit in which the inputs of theinformation signals are exchanged in accordance with the time.

A composite optical distribution circuit 40-5 comprises an opticalexchange switch 9 and the optical distribution circuit 6. Theinformation signals 1 are inputted to the optical exchange switch 9 andare outputted while exchanging the order in accordance with theselection frequencies of the information signals 1. Output signals ofthe optical exchange switch 9 are inputted to the optical distributioncircuit 6 whose scale is reduced by using differences of the selectionfrequencies. In the optical distribution circuit 6, an arbitraryinformation signal 1 to each subscriber is selected and outputted as adistribution signal 4.

According to the embodiment, the scale can be effectively reduced in asystem in which information having selection frequencies which changewith the elapse of time is distributed.

When a photosignal is handled as a data train which was digitized, aplurality of information can be outputted as one signal by time divisionmultiplexing. FIGS. 28A and 28B show a construction of input and outputsignals of the optical distribution circuit used in a time-divisionmultiplexing technique and a time change of each signal.

Three information signals 1 of A, B, and C are inputted to the opticaldistribution circuit 6 and are controlled by three control signals 15 ofA, B, and C and are outputted as distribution signal 4. As shown in FIG.28B, each of the information signals 1 is synchronized by a perioddivided by broken lines. For example, in the case of the informationsignal A, the signal comprising a combination of data trains A0, A1, A2,and A3 is repetitively outputted four times for the period of timedivided by the broken lines and is sequentially outputted in accordancewith the order. In the case of the information signal B as well, thesignal is similarly repetitively outputted four times. In the case ofthe information signal C, a data train of a length that is about twiceas long as the above data train is repetitively outputted twice. Thosethree control signals 15 are matched with each data train which isselected and are set into the separation mode so as not to be overlappedwith the other control signals with respect to time. The output signalwhich is outputted as a distribution signal 4 is a signal in which threeinformation signals were time-division multiplexed.

The embodiment can provide a plurality of information signals to onesubscriber by time-division multiplexing the synchronized data train byusing the information signals.

In the invention shown by the embodiment, the number of inputs and thenumber of outputs are not limited to 3 and 1, respectively, but theinvention also can be applied to a larger number of input and outputsignals. A length of period to be synchronized and the number ofrepetition times are also not limited to those shown in the embodimentbut also can be arbitrarily set.

An embodiment in which the photosignal which was wavelength-divisionmultiplexed or frequency-division multiplexed is distributed will now bedescribed. FIG. 29 shows a construction in which the wavelength-divisionmultiplexed signal is distributed. Three information signals 1 of A, B,and C are inputted to the optical distribution circuit 6. Theinformation signals A, B, and C have different wavelengths λa, λb, andλc. The control signals 15 corresponding to the information signals A,B, and C are the control signals A, B, and C and input the separationmode, non-separation mode, and separation mode, respectively. Thesignals A and B in the separation mode are wavelength-divisionmultiplexed and outputted as a distribution signal 4.

According to the embodiment, by using the information signals ofdifferent wavelengths, the wavelength-division multiplexed signal can bedistributed to the subscriber.

In the invention shown by the embodiment, the number of inputs and thenumber of outputs are not limited to 3 and 1, respectively, but theinvention also can be applied to a larger number of input and outputsignals. The number of signals which can input the separation modes isalso not limited to 2 but also can be arbitrarily set.

Further, an arbitrary photosignal in which wavelength characteristics ofthe light power dividing and propagation direction changing means 20 andwavelength characteristics of the optical amplifying sections 16 and 17lie within an almost predetermined wavelength range can be used.

FIG. 30 shows a fundamental construction for explaining the effect ofscale reduction in the optical distribution circuit 6 of the invention.An optical distribution circuit 6-13 in the embodiment comprises: anoptical distribution device 10-12 having (k1) first optical paths and(h1) second optical paths; and an optical distribution device 10-13having (h1) first optical paths and (h2) second optical paths.

(k1) information signals 1 are inputted to the optical inputs 11 of theoptical distribution device 10-12 and (h1) signals are selected from the(k1) signals. The selected (h1) photosignals are outputted from theoptical outputs 14 and inputted to the optical inputs 11 of the opticaldistribution device 10-13. The optical distribution device 10-13 outputsthe distribution signals 4 from the (h2) optical outputs 14 in order todistribute the signals to (h2) subscribers of the number larger than thenumber (h1) of signals.

The (k1) information signals 1 can be distributed to the (h2)distribution signals 4. Since k1>h1 and h1<h2, the scale in which theoptical distribution circuits of (k1×h2) are needed in the matrix typecan be realized by the two small optical distribution circuits 10 of(k1×h1) and (h1×h2).

FIG. 31 shows an embodiment in which the method of constructing thedistribution circuit in the present invention was applied to a timeswitch.

The embodiment comprises: a request control circuit 50; an informationmemory 51 having (h) memory cells; a write control circuit 52; and aread control circuit 53. The request control circuit 50 controls thewrite control circuit 52 and the read control circuit 53 in accordancewith the inputted request signal 5. The write control circuit 52 inputsthe information signal 1 in which (m) data trains were time-divisionmultiplexed and writes the data train of the selected channel into thememory cell in the information memory 51 which was designated by therequest control circuit 50. In a switch in which all of the channels arefrequently selected, it is necessary that the values of (h) and (m) areequal. In the case where all of the channels are not always selected,however, it is possible to use the (h) memory cells of the number whichis smaller than (m) and (h) denotes the maximum number of channels whichcan be selected. The read control circuit 53 outputs the distributionsignal 4 in which (n) data trains were time-division multiplexed. In thecase of outputting the time-division multiplexed signal at same speed asthat of the information signal 1 which is inputted, the values of (m)and (n) are equal.

In the conventional time switch, the values of (m), (n), and (h) areequal. In the embodiment, when the subscriber who selects the samechannel, even in the case where the values of (m) and (n) are equal, thesystem can operate even if the value of (h) is smaller than the value of(m:m=n).

In the case where a probability such that the channels to be selectedare overlapped as in the cable television system is large, the value of(h) can be suppressed to a small value. On the other hand, when thenumber (n) of outputs is set to the maximum number of viewers and thetime-division multiplexed signal is spatially distributed, by skippingthe subscribers who are not watching and listening to the televisionprogram, the scale can be reduced.

According to the present invention as mentioned above, since thefunctions to distribute and select the photosignal can be realized bylight power dividing and propagation direction means, the device can beminiaturized. On the other hand, according to the invention, since onlythe selected and separated photosignal is optically amplified, thesignal which is not selected is not amplified. Therefore, there is aneffect such that electric power consumption is suppressed. Moreover,there is also an effect such that in the case where the number ofchannels and the number of subscribers is increased, by additionallyarranging optical distribution devices for coping with such increases innumbers to the optical distribution circuit which has already beeninstalled, the system can easily cope with such a case.

In an optical distribution circuit of the matrix type, where the numberof channels and the number of subscribers are increased so that thescale is too large in the matrix type optical distribution circuit,there is an effect such that the circuit scale is reduced by the methodof synthesizing the distribution circuit according to the invention.Further, even in a general distribution switch such as a space switch ortime switch, the scale can be also effectively reduced by thedistribution circuit synthesizing method of the invention.

In the optical distribution circuit according to the invention, manykinds of connections according to the system which is used can be easilyperformed. By using a construction suitable for the system, there is aneffect such that the circuit scale can be effectively reduced.

The optical distribution circuit according to the invention also can beapplied to a time-division multiplexing system or a wavelength-divisionmultiplexing system.

Although, the present invention has been described in detail, it shouldbe understood that various changes, substitutions and alterations can bemade hereto without departing from the spirit and scope of the presentinvention as defined by the appended claims.

What is claimed is:
 1. An optical distribution system comprising:anoptical signal supplier for supplying at least m photosignals; anoptical signal delivery circuit for delivering at least n photosignals;and a time switch having m inputs connected to said optical signalsupplier and n outputs connected to said optical signal deliverycircuit, said time switch comprising: a memory having h memory cells,wherein m>h and n>h, wherein h, m, and n are integers, a writecontroller, operatively associated with said memory, which controlswriting from said m inputs to said h memory cells, and a readcontroller, operatively associated with said memory, which controlsreading from said h memory cells to said n outputs.
 2. An signaldistribution system comprising:a signal supplier for supplying at leastm signals; a signal delivery circuit for delivering at least n signals;and a time switch having m inputs connected to said signal supplier andn outputs connected to said signal delivery circuit, said time switchcomprising: a memory having h memory cells, wherein m>h and n>h, whereinh, m, and n are integers a write controller, operatively associated withsaid memory, which controls writing from said m inputs to said h memorycells, and a read controller, operatively associated with said memory,which controls reading from said h memory cells to said n outputs.